1. Field of the Invention
The present invention relates to a throw-away tip which is detachably mounted on a tool body of a throw away cutting tool for use in various cutting operations.
2. Description of the Related Art
As a throw-away tip of this type, one is generally known in which a plate-like tip body has a major surface formed as a rake face and a peripheral surface formed as a flank face, and a cutting edge formed at the crossing ridge between the rake face and the flank face. Recently, a so-called CBN tip has been widely used in which the cutting-edge portion is formed of high hardness CBN (cubic boron nitride). Such a CBN tip, although having high hardness, lacks toughness and is fragile compared with hard metal or the like, and is susceptible to chipping and breaking. Therefore, especially with such a CBN tip, for the purposes of preventing chipping and breaking, the above cutting-edge-forming ridge is subjected to honing to form a chamfered surface. In such honing, it is a common practice to provide a plane chamfered surface which crosses the rake face and the flank face at an obtuse angle or to provide a rounded surface of an arc shape in section perpendicular to the cutting-edge-forming ridge. There is also a case where the honing is effected to provide, as shown in FIG. 4, a plane chamfered surface 1 and a rounded surface 3 at the crossing ridge between the plane chamfered surface 1 and a flank face 2.
These conventional throw-away tips, however, have the following drawbacks. First, where the honing is effected to provide only the plane chamfered surface, because its angle is still acute, the crossing ridge portion between the chamfered surface and the rake face, and between the chamfered surface and the flank face is susceptible to chipping in spite of the honing. Next, because of the hardness of CBN, a sufficiently large honing width may not be obtained with the present honing-to-round technique. Therefore, where only the honing-to-round is effected, a honing width that exceeds 0.07 mm, for example, which is usually required, may not be attained without an extensive honing cost, making it industrially impractical.
On the other hand, as shown in FIG. 4, where the honing is effected to provide the rounded surface 3 in addition to the plane chamfered surface 1, a large round-honing width is not required as compared with round-honing the entire surface to be chamfered. Also in this case, however, to improve the toughness of the cutting edge, the radius R of the honed rounded surface 3 as in the section as referred to above must be enlarged, resulting in the throw-away tip having a greatly reduced wear resistance. Especially when working on hardened steel, fins are likely to be produced. In contrast, if the above radius R is small, the effect of improving the toughness of the cutting edge becomes small, resulting in an insufficient improvement in resistance to chipping or breaking.
The present invention has been made to overcome the above drawbacks, and accordingly, it is an object of the present invention to provide a throw-away tip which has an improved wear resistance and a tough cutting edge, prevents occurrence of fins, and enables suppression of chipping and breaking.
In order to attain the above object, according to the present invention, there is provided a throw-away tip which comprises a tip body with a rake face and a flank face; a generally plane chamfered surface formed at and along a cutting-edge-forming ridge where the rake face and the flank face cross each other; and a phantom radius surface formed at a crossing ridge between the chamfered surface and the flank face, the phantom radius surface being constituted, as in section perpendicular to the cutting-edge-forming ridge, by a plurality of lines connected to one another to provide a generally convex shape.
In the thus constructed throw-away tip, because the phantom radius surface in section is formed in a bent-back but generally convex shape from the chamfered surface to the flank face, an improvement in wear resistance may be made as compared with a throw-away tip in which the region between the chamfered face and the flank face is round-honed. Furthermore, because each crossing angle of neighboring lines is on the average larger than the crossing angle of the chamfered surface and the flank face, the toughness of the cutting edge is improved, and a reduction may be made in the processing cost. Incidentally, such a phantom radius surface may be formed with ease by grinding the tip body with a brush adhered with, for example, loose grains of a material such as diamond.
It is desirable that the radius of an arc approximated to the plurality of lines connected in a generally convex shape as in the section perpendicular to the cutting-edge-forming ridge, or the phantom radius R of the phantom radius surface in section is in the range of from 0.02 to 0.07 mm. If the radius is less than the above, the crossing angle of neighboring lines becomes small, resulting in an impaired improvement in resistance to chipping, while in contrast, if it exceeds the above range, there arises a fear that the improvement in wear resistance will be impaired.
Preferably, the phantom radius surface is constituted, in the section perpendicular to the cutting-edge-forming ridge, by a plurality of straight lines, neighboring ones of which cross each other in a convex manner. In this way, the wear resistance and the cutting-edge toughness may be more effectively improved. In this instance, the number of the straight lines, as in section perpendicular to the cutting-edge-forming ridge, constituting the phantom radius surface, is preferably at least three. If the phantom radius surface in section is formed by two or less straight lines, the crossing angle of the two straight lines becomes small, possibly resulting in an impaired improvement in resistance to chipping. Furthermore, in this instance, the radius of an arc as in the section perpendicular to the cutting-edge-forming ridge, which extends through an intersection point between the phantom radius surface and the chamfered surface, an intersection point between the phantom radius surface and the flank face, and crossing points of neighboring ones of the straight lines constituting the phantom radius surface, is preferably in the range of from 0.02 to 0.07 mm.
Preferably, the surface-roughness of the rake face is xc2xd or less of the surface-roughness of the flank face within a region of 100 xcexcm from the crossing ridge between the flank face and the phantom radius surface. In this way, a smooth flow of chips produced during cutting work is achieved, thereby preventing the occurrence of welding on the cutting edge and the rake face. More specifically, it is preferred that the surface-roughness of the rake face be in the range of from Rmax 0.01 to 2.0 xcexcm, and that the surface-roughness of the flank face be in the range of from Rmax 0.1 to 5.0 xcexcm.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.